1. Field of the Invention
The present invention relates to a facility for monitoring a low level radio-frequency signal, particularly in radio navigation equipment such as the widely used ILS (Instrument Landing System).
2. Description of the Prior Art
A facility of the kind to which the invention applies is described in an article by H-Rausch, "Moderne Funk-Landesysteme", Elektronik-Anzeiger, 6th Year, 1974, No. 11, pp. 223 to 227.
A monitoring facility forms part of the monitoring system described in the aforementioned references, the monitor being intended for an instrument-landing system (ILS). The signals to be monitored (if picked up, for example, by monitoring dipoles located at a distance of 100 m from the transmitter) may have such a small amplitude that they must be amplified prior to evaluation. To permit correct monitoring, an amplifier is needed which maintains the required gain stability over a long period and is substantially independent of temperature. Such amplifiers are complicated and susceptible to malfunction.